Minnesota cancels invasive moth treatment after federal funds cut

For the first time in two decades, Minnesota will not spray this spring to slow the spread of an invasive moth that has been threatening the state’s forests.

The state never received promised funds for the annual treatment against spongy moth — formally called gypsy moth — from the U.S Department of Agriculture, putting the future of the program, and thousands of acres of woods, at risk.

The funding has been delayed under the Trump administration and it is uncertain when, if, at all, it will come through, according to a statement from the Minnesota Department of Agriculture.

There is only a small window of time in the spring when the pesticide is effective at killing the invasive caterpillars — almost immediately after they hatch in May, said Mark Abrahamson, the plant protection division director for the Minnesota Department of Agriculture (MDA).

The state is hopeful some of the funds will be released by the end of the year to allow it to continue a vital summertime survey that shows foresters where in the state the moth is starting to spread.

USDA officials did not respond to requests for an interview.

The state had been planning to spray a total of 2,700 acres of forests in Anoka, Carlton, Itasca, St. Louis and Winona counties.

Spongy moths are native to Europe and have been working westward since infesting the east coast more than a century ago. They can devastate more than 300 types of host trees and shrubs in North America, eating off their leaves and causing widespread defoliation. They seem to target oaks, birch and aspen, Abrahamson said.

Their destructiveness comes from their sheer numbers. Female spongy moths will lay anywhere between 500 and 1,000 eggs at a time, causing major booms in caterpillars that can quickly eat their way through wide swaths of a forest’s canopy.

While the bugs rarely kill the trees outright, they often stress them out to the point that the trees cannot fight off other pests or diseases, which finish them off, Abrahamson said.

“They defoliate big areas and leave a real mess,” he said.

While the moths have infested much of northern and western Wisconsin, Minnesota has been able to largely fight off any major outbreaks since the 1980s.

Since 2004, the moth has been primarily held at bay through the state’s partnership with the federal “Slow the Spread” program. Each summer, foresters and entomologists head out into the woods with pheromone traps to survey for where small populations of the invaders are likely to boom.

They then target those areas the next spring, spraying them with the bacterial pesticide thuringiensis kurstaki (BtK), which kills off young caterpillars. The state comes back a few months later to spray the site with more pheromones, which work to keep adult mating moths from finding each other and laying more eggs.

Missing a year of spraying could allow the bugs to get a foothold in new parts of the state, allowing small pioneering populations that could still be eradicated to grow into established territory.

Once established they will “advance quicker into neighboring areas, making future years of management more complicated and costly,” said MDA Commissioner Thom Petersen.

The most important thing is to make sure that state foresters can still do the annual survey this summer, Abrahamson said.

The state can bounce back from missing a year of spraying, even if it is more costly and complicated, so long as foresters know where to spray. But without the survey, the state will fall years behind, he said.

The funding delay comes as the Trump administration has cut more than $220 million in federal grants. Minnesota Gov. Tim Walz has told state agencies to start planning as if all of their federal funding will be eliminated. The state Department of Health laid off 170 employees and rescinded job offers for nearly 20 others as a result of the canceled grants.